1. Field of the Invention
Prefabricated thermal insulated tubing has wide ranging application in industry, and in particular the chemical process industry, wherein fluids passing through metallic or plastic tubing must be maintained as closely as possible to specified temperatures during flow over substantial distances, often in hostile environments. In such instances, the fluid must be protected against wide excursions of ambient temperature conditions. Common protective methods involve applying insulation about the tubing, for example by coating the tubing with insulation by an extrusion process and/or by applying successive layers of materials having inherently low thermal conductivity properties.
The present invention is thought to be properly classified in the field of tubing, pipe or conduit products of the type thermally insulated through the provision of distinct layers or wraps of thermal insulation materials.
2. Description of the Prior Art
In applying successive layers of materials, by a process described as "taping" to those knowledgeable in the wire and cable industry, great care is exercised, typically, to maintain a smooth covering of the taping materials. By means of this careful, smooth application, voids are minimized and dielectric strength is maximized.
This is generally accomplished by proper adjustment of the tape let-off device, tape-pad holder, so that the angle formed between the horizontal and the tape being dispensed is equal to the angle of the tape being applied to the substrate being taped. The required angles for a given condition of tape application are readily calculated from geometrical considerations of the tape overlap, the width of the tape, the thickness of the tape, the resiliency of the tape, and the dimensions of the object being taped.
In contrast, an essential goal of thermal insulating materials is to introduce as much air into the volume as is possible, consistent with other mechanical or dimensional properties required for the product. Thus, it becomes possible to reduce the thermal conductivity properties of the insulating material, thereby increasing the efficiency of the thermal insulation.
Thermally insulated tubing products are disclosed, for example, in U.S. Pat. Nos. 3,269,422; 3,400,737; and 3,315,703. Typically, such products are produced by manufacturers of heavy duty wire and cable, since their machinery is well suited for manufacturing both thermally insulated, jacketed tubing and electrically insulated, jacketed wire and cable.
However, as noted above, the taping procedures normally employed in producing electrical cable, though well suited for that purpose, do not serve to achieve the above stated goal in the manufacture of tubing products carrying fluids the temperature of which is to be maintained, namely, the goal of introducing air into the volume of insulation to reduce the normal thermal conductivity properties of the insulating wrap.